U.S. patent application number 15/701155 was filed with the patent office on 2017-12-28 for engine error detection system.
The applicant listed for this patent is Tula Technology Inc.. Invention is credited to Shikui Kevin CHEN, Li-Chun CHIEN, Masaki NAGASHIMA.
Application Number | 20170370804 15/701155 |
Document ID | / |
Family ID | 60675027 |
Filed Date | 2017-12-28 |
United States Patent
Application |
20170370804 |
Kind Code |
A1 |
CHEN; Shikui Kevin ; et
al. |
December 28, 2017 |
ENGINE ERROR DETECTION SYSTEM
Abstract
A variety of methods and arrangements for detecting misfire and
other engine-related errors are described. In one aspect, a window
is assigned to a target firing opportunity for a target working
chamber. There is an attempt to fire a target working chamber
during the target firing opportunity. A change in an engine
parameter (e.g., crankshaft angular acceleration) is measured
during the window. A model (e.g., a pressure model) is used to help
determine an expected change in the engine parameter during the
target firing opportunity. Based on a comparison of the expected
change and the measured change in the engine parameter, a
determination is made as to whether an engine error (e.g., misfire)
has occurred.
Inventors: |
CHEN; Shikui Kevin; (San
Jose, CA) ; NAGASHIMA; Masaki; (Pacific Grove,
CA) ; CHIEN; Li-Chun; (Milpitas, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Tula Technology Inc. |
San Jose |
CA |
US |
|
|
Family ID: |
60675027 |
Appl. No.: |
15/701155 |
Filed: |
September 11, 2017 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14880652 |
Oct 12, 2015 |
9784644 |
|
|
15701155 |
|
|
|
|
62064786 |
Oct 16, 2014 |
|
|
|
62148636 |
Apr 16, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02D 41/0087 20130101;
F02D 2200/1015 20130101; F02D 41/22 20130101; F02D 41/0097
20130101; F02D 2200/1012 20130101; G01M 15/11 20130101; F02D 35/024
20130101 |
International
Class: |
G01M 15/11 20060101
G01M015/11; F02D 35/02 20060101 F02D035/02; F02D 41/22 20060101
F02D041/22 |
Claims
1. A method for detecting misfire in an engine, the engine having a
plurality of working chambers and being operated in a skip fire
manner, the method comprising: assigning a window to a target
firing opportunity; attempting to fire a target working chamber
during the target firing opportunity; measuring a change in an
engine parameter during the target firing opportunity; using a
multi-cylinder pressure model to help determine an expected change
in the engine parameter during the target firing opportunity
wherein the pressure model involves estimating pressure in a
skipped working chamber, wherein the determination of the expected
change in the engine parameter accounts for torque added or
subtracted from the powertrain by an auxiliary power source; based
on a comparison between the expected change and the measured
change, determining whether the target working chamber
misfired.
2. A method as recited in claim 1 wherein the engine parameter is
crankshaft acceleration.
3. A method as recited in claim 1 wherein the multi-cylinder
pressure model involves modeling pressure within each working
chamber during a time period between intake valve closure and
exhaust valve opening of the target firing opportunity.
4. A method as recited in claim 1 wherein the pressure model takes
into account at least one selected from the group consisting of a
rise of temperature in a working chamber due to combustion, fuel
mass used to fuel combustion, energy conversion efficiency,
ignition timing, residual fraction, leakage rate, fuel properties
such as heating value, and total mass of mixture in a working
chamber.
5. A method as recited in claim 1 further comprising using the
pressure model to determine an expected torque generated by the
working chambers of the engine during the target firing
opportunity.
6. A method as recited in claim 1 wherein the determination of the
misfire is based at least in part on A, B and A' wherein A is the
expected change in the engine parameter based on the model, A' is
one of an expected change in the engine parameter based on mass air
charge and a low-pass filtered mean of A and B is the measured
change in the engine parameter.
7. A method as recited in claim 1 further comprising: detecting a
first offset between the estimated expected change and the measured
change in the engine parameter; adjusting the pressure model based
on the first offset; and repeating the pressure model usage and
measurement operations, thereby providing a second expected change
and a second measured change in the engine parameter wherein a
second offset between the second expected change and the second
measured change is reduced relative to the first offset as a result
of the model adjustment.
8. A misfire detection system for determining whether a particular
working chamber in an engine has misfired, the engine being
operated in a skip fire manner, the misfire detection system
comprising: an engine parameter measurement module that is arranged
to: assign a window to a target firing opportunity; and measure a
change in an engine parameter during the target firing opportunity;
and a misfire detection module that is arranged to: use a pressure
model to help determine an expected change in the engine parameter
during the target firing opportunity wherein the pressure model
involves estimating pressure in a skipped working chamber, wherein
the determination of the expected change in the engine parameter
accounts for torque added or subtracted from the powertrain by an
auxiliary power source; and determine whether the target working
chamber misfired based on a comparison between the expected change
and the measured change.
9. A misfire detection system as recited in claim 8 wherein the
engine parameter is crankshaft acceleration.
10. A misfire detection system as recited in claim 8 wherein the
pressure model involves modeling pressure within a working chamber
during a time period between intake valve closure and exhaust valve
opening.
11. A misfire detection system as recited in claim 8 wherein the
multi-cylinder pressure model takes into account at least one
selected from the group consisting of a rise of temperature in a
working chamber due to combustion, fuel mass used to fuel
combustion, energy conversion efficiency, ignition timing, residual
fraction, leakage rate, fuel properties such as heating value, and
total mass of mixture in a working chamber.
12. A misfire detection system as recited in claim 8 wherein the
misfire detection module is further arranged to determine an
expected torque generated by the working chambers of the engine
during the firing opportunity.
13. A misfire detection system as recited in claim 8 wherein the
misfire determination is based at least in part on A, B and A'
wherein A is the expected change in the engine parameter based on
the model, A' is one of a low-pass filtered mean of A and an
expected change in the engine parameter based on mass air charge,
and B is the measured change in the engine parameter.
14. A misfire detection system as recited in claim 8 wherein the
misfire detection module is further arranged to: detect a first
offset between the estimated expected change and the measured
change in the engine parameter; adjust the pressure model based on
the first offset; and repeat the pressure model usage and
measurement operations, thereby providing a second expected change
and a second measured change in the engine parameter wherein a
second offset between the second expected change and the second
measured change is reduced relative to the first offset as a result
of the model adjustment.
15. A method for detecting misfire in an engine, the engine having
a plurality of working chambers and being operated in a dynamic
firing level modulation manner, the method comprising: assigning a
window to a target firing opportunity; attempting to fire a target
working chamber during the target firing opportunity; measuring a
change in an engine parameter during the target firing opportunity;
using a multi-cylinder pressure model to help determine an expected
change in the engine parameter during the target firing opportunity
wherein the pressure model involves estimating pressure in a
skipped working chamber; and based on a comparison between the
expected change and the measured change, determining whether the
target working chamber misfired.
16. A method as recited in claim 15 wherein a cam actuated intake
valve controls air induction into a cylinder, the cam having a cam
profile, and the multi-cylinder pressure model uses different
inputs for different cylinders depending on the cam profile.
17. A method as recited in claim 15 wherein the model of the
expected change in the engine parameter during the target firing
opportunity accounts for torque added to or subtracted from the
powertrain by an auxiliary power source.
18. A method as recited in claim 15 wherein the method is performed
during dynamic multi-charge level operation of the engine.
19. A method as recited in claim 15 wherein the method is performed
during multi-level skip fire operation of the engine.
20. A misfire detection system for determining whether a particular
working chamber in an engine has misfired, the engine being
operated in a dynamic firing level modulation manner, the misfire
detection system comprising: an engine parameter measurement module
that is arranged to: assign a window to a target firing
opportunity; and measure a change in an engine parameter during the
target firing opportunity; and a misfire detection module that is
arranged to: use a pressure model to help determine an expected
change in the engine parameter during the target firing opportunity
wherein the pressure model involves estimating pressure in a
skipped working chamber; and determine whether the target working
chamber misfired based on a comparison between the expected change
and the measured change.
21. A misfire detection system as recited in claim 20 wherein a cam
actuated intake valve controls air induction into a cylinder, the
cam having a cam profile, and the multi-cylinder pressure model
uses different inputs for different cylinders depending on the cam
profile.
22. A misfire detection system as recited in claim 20 wherein the
model of the expected change in the engine parameter during the
target firing opportunity accounts for torque added to or
subtracted from the powertrain by an auxiliary power source.
23. A misfire detection system as recited in claim 20 arranged to
detect misfires during multi-charge level operation of the
engine.
24. A misfire detection system as recited in claim 20 arranged to
detect misfires during multi-level skip fire operation of the
engine.
25. A method as recited in claim 1 wherein the auxiliary power
source is an electric motor/generator.
26. A misfire detection system as recited in claim 8 wherein the
auxiliary power source is an electric motor/generator.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation-in-Part of U.S. patent
application Ser. No. 14/880,652, entitled "Misfire Detection in a
Dynamic Skip Fire Engine," filed Oct. 12, 2015, which claims
priority of U.S. patent application Ser. No. 62/064,786, entitled
"Misfire Detection in a Dynamic Skip Fire Engine," filed Oct. 16,
2014; and U.S. patent application Ser. No. 62/148,636, entitled
"Engine Error Detection System," filed Apr. 16, 2015, each of which
is incorporated herein in its entirety for all purposes.
FIELD OF THE INVENTION
[0002] The present invention relates generally to powertrain
diagnostics. Various embodiments pertain to a misfire detection
system and an adaptive model for detecting engine- or working
chamber-related errors
BACKGROUND
[0003] Skip fire engine control is understood to offer a number of
benefits including the potential of increased fuel efficiency. In
general, skip fire engine control contemplates selectively skipping
the firing of certain cylinders during selected firing
opportunities. Thus, for example, a particular cylinder may be
fired during one firing opportunity and then may be skipped during
the next firing opportunity and then selectively skipped or fired
during the next. This is contrasted with conventional variable
displacement engine operation in which a fixed set of the cylinders
are deactivated during certain low-load operating conditions.
[0004] In this manner, even finer control of the effective engine
displacement is possible. For example, firing every third cylinder
in a 4 cylinder engine would provide an effective displacement of
1/3.sup.rd of the full engine displacement, which is a fractional
displacement that is not obtainable by simply deactivating a set of
cylinders. Similarly, firing every other cylinder in a 3 cylinder
engine would provide an effective displacement of 1/2, which is a
fractional displacement that is not obtainable by simply
deactivating a set of cylinders. U.S. Pat. No. 8,131,445 (which was
filed by the assignee of the present application and is
incorporated herein by reference in its entirety for all purposes)
teaches a variety of skip fire engine control implementations.
[0005] When a cylinder is deactivated in a variable displacement
engine, its valves are not actuated and although the piston
typically still reciprocates, fuel is not combusted during the
power stroke. Since the cylinders that are "shut down" don't
deliver any net positive torque, the proportionate load on the
remaining cylinders is increased, thereby allowing the remaining
cylinders to operate at an improved thermodynamic efficiency. With
skip fire control, cylinders are also preferably deactivated during
skipped working cycles in the sense that air is not pumped through
the cylinder and no fuel is delivered and/or combusted during
skipped working cycles when such valve deactivation mechanism is
available. Often, no air is introduced to the deactivated cylinders
during the skipped working cycles thereby reducing pumping losses.
However, in other circumstances it may be desirable to trap exhaust
gases within a deactivated cylinder, or to introduce, but not
release air from a deactivated cylinder during selected skipped
working cycles. In such circumstances, the skipped cylinder may
effectively act as a gas spring. Although deactivating skipped
cylinders is generally preferred, it should be appreciated that in
some engines or during some working cycles it may not be possible,
or in some situations desirable, to truly deactivate cylinders.
When a cylinder is skipped, but not deactivated, intake gases drawn
from the intake manifold are effectively pumped through the
cylinder during the skipped working cycle.
[0006] Although the concept of skip fire control has been around
for a long time, it has not traditionally been used in commercially
available engines, so an additional challenge to implementing skip
fire control is insuring that the engine's other engine/power train
systems work effectively during skip fire control. One such system
relates to engine diagnostics. As is well understood by those
familiar with the art, modern vehicles incorporate engine
management systems that perform in-situ diagnostics on various
powertrain and vehicle component during vehicle operation. These
diagnostic systems are often referred to as "On-Board Diagnostics"
(OBD) systems and there are a number of engine diagnostic protocols
that are performed while the engine is running. Modern OBD systems
store and report a significant amount of information concerning the
operation and state of health of various vehicle sub-systems
including the powertrain. For example, some OBD systems are
arranged to detect a situation in which a cylinder misfires i.e.,
when the cylinder fails to fire or there is incomplete combustion
in the cylinder.
[0007] Although prior art OBD systems are well suited to detect
misfire in a conventional all-cylinder engine control system, they
are generally ill suited for use in a skip fire engine control
system. Various embodiments of the present invention contemplate
arrangements, methods and techniques for detecting misfire in an
engine operated in a skip fire manner
SUMMARY
[0008] A variety of methods and arrangements for detecting misfire
and other engine-related errors in an internal combustion engine
are described. In one aspect, a window is assigned to a target
firing opportunity for a target working chamber. In various
embodiments, the window is related to the rotation of the
crankshaft. There is an attempt to fire a target working chamber
during the target firing opportunity. A change in an engine
parameter (e.g., crankshaft angular acceleration or another
crankshaft-related parameter) is measured during the window. A
model (e.g., a multi-cylinder pressure model) is used to help
determine an expected change in the engine parameter during the
target firing opportunity. In various embodiments, the engine is
operated in a dynamic firing level modulation manner where
purposefully different air charges and corresponding fueling levels
are associated with different firing opportunities. In other
embodiments, an auxiliary power source adds or subtracts torque
from the crankshaft in addition to the engine supplied torque.
Based on a comparison of the expected change and the measured
change in the engine parameter, a determination is made as to
whether an engine- or working chamber-related error (e.g., misfire)
has occurred. In various embodiments, the model is adjusted
dynamically based on the measured change in the engine parameter to
help improve the accuracy of the model.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The invention and the advantages thereof, may best be
understood by reference to the following description taken in
conjunction with the accompanying drawings in which:
[0010] FIG. 1 is a flow diagram illustrating a method of detecting
misfire in a skip fire engine control system according to a
particular embodiment of the present invention.
[0011] FIG. 2 is a block diagram of a misfire detection system
according to a particular embodiment of the present invention.
[0012] FIG. 3 is a block diagram of firing opportunities and
associated angular window segments according to a particular
embodiment of the present invention.
[0013] FIG. 4 is a block diagram of a misfire detection system
according to a particular embodiment of the present invention.
[0014] FIG. 5 is a graph of cylinder pressure as a function of
crank angle according to a particular embodiment of the present
invention.
[0015] FIG. 6 is a graph of cylinder pressure as a function of
cylinder volume according to a particular embodiment of the present
invention.
[0016] FIG. 7 is a graph comparing a modeled cylinder pressure and
a measured cylinder pressure according to a particular embodiment
of the present invention.
[0017] FIG. 8 is a graph of crankshaft acceleration as a function
of time according to a particular embodiment of the present
invention.
[0018] FIG. 9 is a flow diagram illustrating a method of detecting
an engine error using an adaptive model according to a particular
embodiment of the present invention.
[0019] FIG. 10 is a graph comparing modeled and measured crankshaft
acceleration using a model according to a particular embodiment of
the present invention.
[0020] FIG. 11 is a graph comparing modeled and measured crankshaft
acceleration using an adaptive model according to a particular
embodiment of the present invention.
[0021] FIG. 12 is a flow diagram illustrating a technique for using
an adaptive model according to a particular embodiment of the
present invention.
[0022] FIG. 13 is a block diagram of a misfire detection system
including an auxiliary power source according to a particular
embodiment of the present invention.
[0023] In the drawings, like reference numerals are sometimes used
to designate like structural elements. It should also be
appreciated that the depictions in the figures are diagrammatic and
not to scale.
DETAILED DESCRIPTION
[0024] The present invention relates to systems for detecting
engine- and working chamber-related errors. More specifically,
various embodiments of the present invention relate to techniques
and arrangements for detecting misfire or other errors in skip fire
engine control systems.
[0025] As noted in the background, prior art misfire detection
systems are generally not suitable for detecting misfire in a
dynamic skip fire engine control system. For example, various prior
art misfire detection systems detect unexpected changes in the
rotation speed of the crankshaft and use this to determine if a
misfire has occurred. This works well in conventional, all cylinder
engine operation, since it is expected that crankshaft acceleration
will remain generally consistent. Although there are some
variations in crankshaft acceleration from one firing to the next,
the crankshaft acceleration peaks and profiles remain generally
consistent in size and shape, in large part due to the fact that
every cylinder is being fired. Thus, when a significant deviation
in crankshaft acceleration is detected with respect to the firing
of a particular cylinder, the misfire detection system may
determine that the cylinder has misfired.
[0026] In dynamic skip fire engine operation, however, any working
chamber or working cycle may be skipped. That is, a particular
working chamber might be fired during one working cycle, skipped
during the next, and fired or skipped during the next. As a result,
the crankshaft acceleration peaks and profiles may abruptly change
as the firing sequence changes, even though all working chambers
are properly firing, i.e. no misfires. Unlike in prior art misfire
detection systems, any substantial drop in crankshaft acceleration
cannot be assumed to indicate a misfire, since in a skip fire
engine control system, selected working cycles may be skipped at
almost any time, each of which may also result in a drop in the
crankshaft acceleration.
[0027] Conventional misfire determination systems also do not
properly take into account the effect that the firing or skipping
of various working chambers have on a measurement of crankshaft
acceleration in a skip fire engine control system. To illustrate
this point, consider an example in which a designated cylinder is
examined for a possible misfire. Combustion takes place in the
designated cylinder during an assigned window (e.g., during at
least part of the combustion stroke for the designated cylinder.)
The crankshaft acceleration is measured during that window. If the
crankshaft acceleration dips below a predetermined threshold, it is
determined that a misfire has occurred in the designated
cylinder.
[0028] In skip fire engine operation, the accuracy of the misfire
determination is improved if the misfire determination system
and/or the misfire threshold takes into account the impact of the
skipping or firing of other cylinders on the measured crankshaft
acceleration. That is, the system should take into account the
firing commands (i.e., skip or fire) for other cylinders that were
executed prior to the window or will be executed after the window.
It should be noted that while the firing of the designated cylinder
may make the largest contribution to the crankshaft acceleration
during the window, there are a number of other factors that affect
crankshaft torque. For example, it requires energy to compress the
intake air during the compression stroke and that energy comes from
the crankshaft thereby acting as a negative torque on the
crankshaft. Engines having multiple cylinders are generally
designed with their working cycles out of phase with one another at
consistent intervals so that the compression of one cylinder occurs
while combustion is occurring in another cylinder. In normal, all
cylinder operation, the torque generated by each firing, the torque
required by each compression stroke, and other engine generated
torques tend to be relatively constant during steady state
operation. Therefore, the even spacing of the cylinder phases tend
to result in each cylinder being affected in much the same way by
events occurring in the other cylinders, which helps contribute to
the consistency between the peaks and profiles associated with each
firing opportunity during normal all-cylinder operation.
[0029] In skip fire operation, the effect of the other cylinders
will not always be so consistent. For example, in some
implementations the valves may be operated in a manner in which the
intake and exhaust valves are opened in the normal sequence during
"fired" working cycles and are both held closed through skipped
working cycles. This will result in the torques applied to the
crankshaft during each stroke of the working cycle being different
during a skipped working cycle than would be seen during a fired
working cycle. Most notably, during a skipped working cycle in
which low pressure exhaust trapping is used, only a small amount of
residual exhaust gases will remain in the cylinder and therefore
the torque imparted during the compression stroke in a skipped
working cycle will be quite different than the torque imparted
during active (fired) working cycles because the relatively large
negative torques required for compression of the intake gases will
be missing during skipped working cycles. The trapped residual
fraction can vary based on the valve timing and MAP influencing the
imparted torque. Since the compression stroke associated with one
cylinder will typically overlap with the combustion stroke of
another, the net torque experienced by the crankshaft during any
particular combustion event will be affected by the firing
decisions of other cylinders. Although the compression stroke tends
to have greatest impact, the differential torques experienced
during the intake and exhaust strokes may also be different in
significant ways. For example, holding the intake valve closed
during the skipped working cycle may cause a very low pressure to
be developed in the cylinder during intake thereby imparting a
larger negative torque during the intake stroke of a skipped
working cycle than would occur during intake of an active (fired)
working cycle.
[0030] Still further, different skip fire controllers may have
different valve actuation schemes and/or may use a combination of
different valve actuation schemes and such valve actuation schemes
can further affect the torque variations experienced by the
crankshaft. For example, if an exhaust valve is not opened after a
combustion event, a "high pressure exhaust gas spring" may
effectively be created within the cylinder combustion chamber by
the combustion gases and the timing of the exhaust valve opening
may be delayed from immediately after the combustion event to a
later working cycle. Such a high pressure spring will have a
significant impact on the torque applied during all of the other
strokes. In another example particularly relevant to direct
injection engines, an intake valve may be opened in a working cycle
in which no fueling or combustion occurs so that an air charge is
trapped within the combustion chamber during a skipped working
cycle. Such events will affect the net torque in yet another way.
In still other circumstances, sometimes referred to as
"re-exhaust", it may be desirable to open the exhaust valve in the
normal course after the firing of a cylinder and then to reopen the
exhaust valve in a subsequent skipped working cycle such as the one
that immediately precedes an active (fired) working cycle resulting
in an extra exhaust valve opening event. In still other
implementations, re-exhaust may be employed at the end of every
skipped working cycle. Of course, a variety of other valve
actuation schemes may be applied as well and it should be apparent
that the timing and magnitude of the torques applied to the
crankshaft will depend on the state of all of the cylinders.
[0031] This application contemplates various techniques for taking
into account at least some of the above factors in making a misfire
determination in a skip fire engine control system. A particular
embodiment contemplates a misfire detection system that detects
misfires using a multi-cylinder pressure model. The pressure model
is used to model the pressure in some or all of the working
chambers during a target firing opportunity. In various
implementations, the pressure model takes into account whether a
working chamber is being fired or skipped, cylinder air charge due
to cam phasing and intake manifold pressure, ignition timing
adjustments and air fuel ratio variation. The pressure modeled for
each working chamber is then used to help determine whether a
particular working chamber is misfiring.
[0032] Referring initially to FIGS. 1 and 2, an example method 100
and system 200 for detecting misfire using a multi-cylinder
pressure model will be described. FIG. 1 is a flow diagram
illustrating the steps of the method 100. The method 100 is
implemented in the misfire detection system 200 illustrated in FIG.
2. The misfire detection system 200 includes a firing timing
determination module 202, a firing control unit 204, an engine
parameter measurement module 206, a misfire detection module 208,
and an engine 250. FIG. 2 illustrates an engine 250 having eight
cylinders, labeled 1 through 8, as the working chambers. Although
engine 250 is shown having 8 cylinders arranged in two banks,
engines having different numbers of cylinders arranged in different
configurations may be used. Also, although a variety of discrete
modules are illustrated in FIG. 2, it should be appreciated that in
various embodiments, the modules may be combined and/or operations
of one module may instead be handled by another module.
[0033] Initially, at step 102 of FIG. 1, firing information is
obtained by the firing timing determination module 202 and/or the
firing control unit 204. The firing timing determination module 202
is arranged to issue a sequence of firing commands used to operate
the engine 250 in a skip fire manner and deliver a desired torque
and/or firing fraction. The skip fire firing sequence may be
determined in a wide variety of ways. For example, the firing
sequence may be generated using a sigma delta converter or any
suitable control algorithm. In some embodiments, the firing
sequence is selected from a library of predefined firing sequences.
The sequence of firing commands is transferred to the firing
control unit 204.
[0034] The firing control unit 204 is arranged to orchestrate the
firings of the working chambers of the engine 250 using the
received firing sequence. The firing control unit 204 receives data
identifying suitable working chambers from any suitable source
(e.g., the engine 250) and matches a selected working chamber to
each firing command Consider a simple example in which the firing
control unit receives a short firing sequence of 0-1-0-0 from the
firing timing determination unit 202, which indicates a skip, fire,
skip and a skip, respectively. In this example, the engine may be
configured so that the cylinder firing opportunities are arranged
in a repeating sequence of 1-8-7-2-6-5-4-3. That is, the first
cylinder to have a firing opportunity may be cylinder 1, followed
by cylinder 8, and then cylinder 7, etc. The firing control unit
204 determines which cylinders should be matched to each firing
command (e.g., it may determine that cylinders 1, 8, 7 and 2 should
be skipped, fired, skipped and skipped, respectively, in accordance
with the sequence.) Various embodiments of the present invention
contemplates using such firing information (i.e., the firing
sequence and the identities or numbers of the corresponding working
chambers) to help detect misfires. Note that the fire/skip
information is typically available before execution of a
firing/skip command, since time is needed to fuel the cylinder and
activate/deactivate the valves.
[0035] At step 104 of FIG. 1, the engine parameter measurement
module 206 assigns windows to each firing opportunity. The window
may be any suitable time period or interval that corresponds to a
target firing opportunity of a target working chamber. A particular
engine parameter will later be measured across the window to help
determine if a misfire has occurred. The characteristics of the
window may differ depending on the type of engine parameter
measurement.
[0036] In one embodiment, for example, the engine parameter to be
measured is crankshaft angular acceleration. The crankshaft angular
acceleration tends to increase when combustion occurs in the target
working chamber. As a result, a suitable window may be one that
covers at least part of the power stroke for the target working
chamber.
[0037] In another embodiment, the engine parameter to be measured
is a combustion exhaust gas property. That is, one or more sensors
in the exhaust system detect levels of oxygen or other components
in an exhaust gas "pulse" that is generated during the firing
opportunity. This analysis is used to help determine whether a
misfire has occurred. This measurement may occur over a different
window. Since exhaust gases are involved, the appropriate window
may cover or correspond to at least a portion of the exhaust stroke
of the target working chamber. Additionally, the window may also
incorporate an offset to account for the time needed for the
corresponding exhaust "pulse" to traverse from the exhaust valve to
the exhaust sensor. Generally, the window may vary widely,
depending on the characteristics of the misfire detection system
200. The exhaust sensor method of sensing misfires may be combined
with the crankshaft acceleration method and other possible means of
misfire detection.
[0038] An example of an association between windows and firing
opportunities for a corresponding working chamber is illustrated in
FIG. 3. In this example, a total of 270.degree. of rotation for the
crankshaft of an eight cylinder, four-stroke engine is shown.
During the rotation, there are three firing opportunities,
corresponding to the firing or skipping of working chambers 1, 8
and 7. A window is assigned to each of the firing opportunities and
working chambers. Each window is an angular window segment that
corresponds to a 90.degree. rotation of the crankshaft. FIG. 3
illustrates an example angular window segment 302, which
corresponds to a firing opportunity for working chamber 8. The
angular window segment 302 begins at or around the time the piston
for the corresponding working chamber reaches top dead center (TDC)
(e.g., at the beginning of a power stroke in a four stroke engine.)
It should be appreciated that the above example is used for
illustrative purposes and that the characteristics of the windows
and the way in which they are assigned may vary for different
applications. For example, it should be appreciated that windows
longer or shorter than 90.degree. rotation of the crankshaft
rotation may used. The length of the window may vary with the
number of cylinders in the engine. For example, longer windows may
be used in engines with fewer cylinders, since there are fewer
firing opportunities per engine revolution. Also, the time windows
associated with each cylinder may overlap.
[0039] Returning to the flow diagram of FIG. 2, the engine
parameter measurement module 206 measures a change in an engine
parameter during the corresponding window (step 106 of FIG. 1) This
measurement may be obtained, for example, using one or more sensors
(e.g., a crankshaft position sensor, an exhaust gas sensor, etc.)
The engine parameter measurement module 206 receives any input or
engine parameter needed to perform the measurement, e.g. engine
speed data, cylinder identity information, firing information from
the firing timing determination module 202/firing control unit 204,
etc. A variety of different engine parameters may be measured
during the window. In some embodiments, for example, a
crankshaft-related parameter or crankshaft angular acceleration is
measured.
[0040] Below is one example formula for calculating crankshaft
angular acceleration for the angular window segment 302 of working
chamber 8 as shown in FIG. 3. In FIG. 3, the angular window segment
302 is divided into two subsegments, earlier subsegment 305b and
later subsegment 305a. The example formula is as follows:
CrankshaftAngularAcceleation = AvgSpeed ( 305 a ) - AvgSpeed ( 305
b ) .DELTA. Time ( 305 ab ) ##EQU00001##
where the AvgSpeed (305a) and AvgSpeed (305b) are the average
velocities of the crankshaft over subsegments 305a and 305b,
respectively, and A Time (305ab) refers to the time needed for the
crankshaft to rotate from the midpoint of subsegment 305b to the
midpoint of subsegment 305a. While the subsegments 305a and 305b
are shown as having equal duration, this need not be the case.
Also, the subsegments 305a and 305b need not be continuous, i.e.
there may be a gap between the segments. The timing of the
subsegments relative to the crankshaft rotation may be adjusted
depending on the engine operating conditions and the misfire
detection algorithm. In some cases more than two subsegments may be
used. The subsegment durations and timing may vary depending on the
engine operating conditions. The average engine speed may be
determined by measuring the lapsed time between reference marks on
the crankshaft passing a fixed reference point. In various
embodiments, the crankshaft reference marks may be equally
distributed around the crankshaft at approximately 6 degree
intervals. The raw signal from crank angle may be processed to
calculate the average speed in a subsegment, acceleration between
subsegments, and the jerk (change in acceleration between pairs of
subsegments). In various embodiments, measurement of jerk requires
use of at least three subsegments, so that a change in acceleration
may be measured. Higher order time derivatives of acceleration may
also be used in misfire determination, with a concomitant increase
in the number of subsegments. Another example method of calculating
crank acceleration is to take a time derivative of raw engine speed
(RPM) signal and apply a bandpass filter such as Type 1 Chebyshev
filter. Various other filtering algorithms may be applied to the
crank signal to improve the accuracy of all these measurements.
Generally, the calculation of engine parameter change is performed
for multiple firing events for each working chamber. Thus, the
engine parameter measurement module builds a history of firing
events for each working chamber, as well as corresponding engine
parameter changes (e.g., crankshaft angular acceleration data) for
the working chamber. This data is later used to help determine
whether a particular working chamber is misfiring or not.
[0041] A variety of engine parameters may be measured in step 106.
In some embodiments, as noted above, a crankshaft-related
parameter, such as the crankshaft angular acceleration or its
derivative (jerk), may be measured. In other embodiments, the
engine parameter measurement involves an analysis of exhaust gases.
For example, as previously discussed, various designs involve
measuring a change in an amount of oxygen in the exhaust of the
engine over a corresponding window or period of time. This change
is associated with a particular target firing opportunity of a
target working chamber. Such changes can provide insight into
whether the target working chamber has misfired.
[0042] The misfire detection module 208 receives the firing
information from the firing control unit 204 and/or the firing
timing determination module 202 and the above engine parameter
measurement data from the engine parameter measurement module 206.
Returning to FIG. 1, at step 108, the misfire detection module 208
uses a pressure model to help determine an expected change in the
engine parameter during the window. This expected change will later
be compared with the change measured in step 106 to determine
whether a misfire has occurred.
[0043] The pressure model is used to model a pressure within each
of the working chambers of the engine during the window. In various
embodiments, the misfire detection module 208 uses the modeled
pressure to estimate the torque generated by the working chamber,
which in turn can be used to help predict a change in the engine
parameter (e.g., crankshaft acceleration) during the window. The
modeling of pressure within multiple working chambers allows the
misfire detection module 208 to take into account the different
operational states of each of the working chambers, and their
corresponding effects on the change in the engine parameter.
[0044] In skip fire engine control systems, the pressure within
each cylinder may vary widely, depending in part on whether a
particular working chamber has or will be skipped or fired. The
skip/fire decision for each working chamber is in the firing
information that the misfire detection module 208 receives from the
firing control unit 204. The misfire detection module 208 is
arranged to use this firing information to model the pressure
within one, some or all of the working chambers during the window.
Any suitable pressure model may be used. A particular
implementation of a pressure model will be described in more detail
later in the application.
[0045] The skipping or firing of a working chamber can have a large
impact on the pressure dynamics within a working chamber during any
given time interval. Consider the example of FIG. 3, in which
during the window 302, working chamber 8 is being fired. In this
example, the working chambers are fired or skipped in the order
1-8-7-2-6-5-4-3. The working cycles of the other working chambers
are out of phase with the working cycle of working chamber 8 at
consistent intervals. Accordingly, while working chamber 8 is in
the first half of a power stroke, working chamber 1 is in the
second half of its power stroke during the same target window 302.
If working chamber 1 is being fired, the combustion process will
tend to substantially increase the pressure in the working chamber.
If working chamber 1 is skipped (e.g., using a low pressure
spring), however, no combustion takes place and the pressure
dynamics within the working chamber will be substantially
different. The pressure model takes into account the different
pressure effects of firing or skipping a working chamber.
[0046] Returning to FIG. 1, at step 110, based on the pressure
model, the misfire detection module 208 determines an expected
change in the engine parameter during the window. This step may be
performed in any suitable manner Various implementations, for
example, involve modeling the pressure within each working chamber
during a particular window and using the modeled pressure to
estimate a torque generated by each working chamber. The modeling
of the torque generated by each working chamber may be based on a
wide variety of engine parameters that feed into the pressure
model. The engine parameters may include, but not limited to, cam
timing, engine speed, mass air charge, cylinder load and manifold
absolute pressure. In various embodiments, the torque generated by
all of the working chambers is summed and used to determine the
expected change in the engine parameter (e.g., crankshaft
acceleration) during the window. Additionally any torque loads
arising from vehicle accessories, such as air conditioning, battery
charging, etc., may be included in the overall torque model. Any
suitable feature of the torque model and associated operations
described in U.S. patent application Ser. No. 14/207,109, which is
incorporated by reference herein in its entirety for all purposes,
may also be used in method 100.
[0047] At step 112, the misfire detection module 208 determines
whether a misfire occurred in the target working chamber during the
target firing opportunity. In various embodiments, this
determination involves comparing the change in the engine parameter
measured in step 106 with the expected change in the engine
parameter determined using the multi-cylinder pressure model (steps
108 and 110). Consider an example in which the engine parameter is
crankshaft acceleration. If a misfire has taken place in the target
working chamber, then combustion in the target working chamber was
incomplete and the crankshaft angular acceleration should be
reduced. In some embodiments, the misfire detection module 208 thus
determines whether the measured change in crankshaft acceleration
falls below the expected change in the crankshaft acceleration
(i.e., as determined using the aforementioned multi-cylinder
pressure model) by a predetermined amount. If so, the misfire
detection module determines that a misfire has (possibly) taken
place in the target working chamber. If not, the misfire detection
module determines that a misfire has not taken place. It should be
appreciated that the above approach is simplified and exemplary and
that a wide variety of methods may be used to make this misfire
determination, some of which will be described later in this
application.
[0048] The use of the pressure model (step 108), the determination
of the expected change in the engine parameter (step 110) and the
misfire determination (step 112) may be performed in a wide variety
of ways. One approach is illustrated in FIG. 4. FIG. 4 is a block
diagram illustrating a technique for calculating an expected change
in crankshaft angular acceleration using a cylinder pressure model.
FIG. 4 includes some of the modules illustrated in FIG. 2 i.e., the
engine parameter measurement module 206 and the misfire detection
module 208. In this example, the misfire detection module 208
includes various submodules i.e., an indicated torque module 460, a
predicted crankshaft acceleration module 480 and a misfire
determination unit 490. It should also be noted that input signal
rationality checks may be performed in each module, in order to
determine integrity of input signals to ensure robustness of the
strategy.
[0049] In the illustrated embodiment, an analytical cylinder
pressure model based on an ideal combustion stroke of an internal
combustion engine is developed to estimate cylinder torque under a
variety of operating conditions including the effects of skip fire
operation (e.g., step 108 of FIG. 1.) The model is applicable to
many types of engine cycles, such as Otto, Atkinson, Miller,
Diesel, etc., using appropriate values that characterize the
combustion event. The model predicts pressure in each cylinder not
only during a fired cycle, but also during skipped cycles. The
modeled cylinder pressure is then used to calculate the indicated
torque based on a simple crank-slider mechanism.
[0050] In this example, a main concept of the analytical pressure
model assumes that the cylinder pressure p(.theta.) modeled as the
interpolation between two asymptotic pressure traces as illustrated
in FIG. 5. The compression stroke 512 is modeled by a polytropic
process characterized by a polytropic exponent k.sub.c and the
thermodynamic state at intake valve closing (IVC). The reference
states at IVC are determined from experimental data. These traces
determine the compression asymptote up until ignition. The
expressions for pressure and temperature for this process are
p c ( .theta. ) = p IVC ( V IVC V ( .theta. ) ) k c ( 1 ) T c (
.theta. ) = T IVC ( V IVC V ( .theta. ) ) k e - 1 ( 2 )
##EQU00002##
[0051] The expansion asymptote 510 is also described by a
polytropic process with polytropic exponent k.sub.e. The quantities
p.sub.3, T.sub.3 and V.sub.3 correspond to point 3 in the ideal
Otto cycle depicted in the pressure-volume (P-V) diagram shown in
FIG. 6. The modeled combustion process moves between points 2 and 3
on the P-V diagram.
p e ( .theta. ) = p 3 ( V 3 V ( .theta. ) ) ? ( 3 ) T e ( .theta. )
= T 3 ( V 3 V ( .theta. ) ) ? ? indicates text missing or illegible
when filed ( 4 ) ##EQU00003##
[0052] The temperature rise .DELTA.T.sub.comb due to combustion is
added to T.sub.2 and state) can be obtained from equation (1) and
(2).
T 3 = T 2 + .DELTA. T comb ( 5 ) p 3 = p 2 ? ( 6 ) .DELTA. T comb =
? ? indicates text missing or illegible when filed ( 7 )
##EQU00004##
[0053] Where fuel mass m.sub.f, heating value q.sub.HV, conversion
efficiency .epsilon., specific heat c.sub.v, and total mass
m.sub.tot are used.
[0054] The interpolation between two asymptotes is the interpolated
pressure 514, based on the pressure ratio approach based on fitting
heat release with the well-known Wiebe function described by
parameters .alpha., start of combustion angle .theta..sub.SOC,
combustion duration .DELTA..theta., and exponent m, which can be
derived from experimental data. The pressure ratio is modeled
by
PR ( .theta. ) = 1 - e ? ? indicates text missing or illegible when
filed ( 8 ) ##EQU00005##
This can then be used for the interpolation
p(.theta.)=(1=PR(.theta.))p.sub.c(.theta.)+PR(.theta.)p.sub.e(.theta.)
(9)
[0055] The procedure above provides a simple and complete model for
pressure between IVC (intake valve closure) and EVO (exhaust valve
opening). The pressure during gas exchange may be set to the intake
manifold pressure. However, for skipped cycles, the pressure will
drop below intake manifold pressure during the intake stroke. To
properly model the pressure evolution during a skipped cycle, a
polytropic process referenced to either the BDC (bottom dead
center) or the exhaust valve closing (EVC) may be used. The
pressure at EVC (exhaust valve closing) for firing cycles may be
derived from experimental data.
p ( .theta. ) = p EVC ( V EVC V ( .theta. ) ) k c ( 10 )
##EQU00006##
[0056] A comparison of the modeled cylinder pressure 804 with the
measured cylinder pressure 802 is shown in FIG. 7. The pressures
during skipped cycles as well as the firing cycles are captured
well enough for accurate torque prediction as described next. For
clarity the initial section of curve 804 (solid line) is omitted
and the final section of curve 802 (dashed line) is omitted.
Inspection of FIG. 7 shows that the model works well in predicting
the cylinder pressure.
[0057] The gas force acting on a piston connected to the crank
shaft by a rod with a crank slider mechanism produces at each
instant an "indicated torque"
T cyl , i ( .theta. ) = ( P cyl , i ( .theta. ) - P crank ) Ar sin
( .theta. + .beta. ) .beta. ( 11 ) .beta. = sin - 1 ? ( 12 ) .PHI.
= sin - 1 ? ? indicates text missing or illegible when filed ( 13 )
##EQU00007##
where p.sub.crank, r, .delta., l and A are crankcase pressure,
crank radius, pin offset, connecting rod length and piston face
cross-section area, respectively. The resultant engine indicated
torque is just sum of the contributions from each cylinder.
T.sub.1(.theta.)=.SIGMA..sub.Namcyl.sup.T.sub.cyl,i(.theta.)
(14)
[0058] The indicated torque may be determined using the methods
described above in the Indicated Torque Module 460 (FIG. 4). Inputs
to the Indicated Torque Module 460 include engine operating
conditions 462, hardware parameters 464, combustion parameters 466,
and a cylinder deactivation flag 468. Engine operating conditions
462 may include engine speed 472, intake manifold absolute pressure
(MAP), intake manifold air temperature, air per cylinder, cam
phasing, and other variables. Hardware parameters 464 may include
connecting rod length, compression ratio, valve opening window, pin
offset and other design parameters. Combustion parameters 466 may
include injection timing, spark timing, heat release
characteristics during combustion and other parameters describing
the combustion details. The cylinder deactivation flag 468
describes whether a cylinder is being fired or skipped.
[0059] The indicated engine torque 474 obtained from using the
cylinder pressure model by the Indicated Torque Module 460 may be
used to determine crank angular acceleration in the Predicted Crank
Acceleration Module 480 (e.g., step 110 of FIG. 1.) The engine
dynamic model used for this derivation is
J eq .theta. + M eq r 2 [ f 1 ( .theta. ) .theta. + f 2 ( .theta. )
.theta. . 2 ] f 3 ( .theta. ) = T i ( .theta. ) - T fp ( .theta. )
- T L ( .theta. ) where ( 15 ) f 1 ( .theta. ) = f 3 ( .theta. ) =
sin .theta. + r 2 l sin 2 .theta. ( 16 ) f 2 ( .theta. ) = cos
.theta. + r l cos 2 .theta. . ( 17 ) ##EQU00008##
.theta. is the crank angle, {dot over (.theta.)} and .theta. are
the angular velocity and the angular acceleration of the
crankshaft, respectively. l is the connecting rod length, and r is
the crank radius. J.sub.sq is the moment of inertia of the
crankshaft, flywheel, gear and rotating part of connecting rod, and
M.sub.sq is the mass of the piston, rings, pin and linear motion
part of the connecting rod. T.sub.i(.theta.), T.sub.fp(.theta.),
and T.sub.L(.theta.) are the indicated engine torque 474, friction
torque 482, and load torque 476, respectively. Other inputs 478,
such as accessory loads, may be considered in Eq. (15). The
derivation of this equation can be found in the literature, for
example Zweiri, et. al. "Instantaneous friction components model
for transient engine operation", Proc. Inst. Mech. Eng. Part J.
Automob. Eng. Vol. 214, no.7 pp. 809-824, July 2000.
[0060] The crank angle e, crank angular velocity{dot over
(.theta.)}, and equivalent mass M.sub.sq may be measured, and the
indicated engine torque T.sub.i(.theta.) 474 is given by the model
previously described. The friction torque T.sub.fp(.theta.) 482 may
be determined by a lookup table obtained from experiments which
relates the crank RPM to friction torque. The combined moment of
inertia of crankshaft, flywheel, gear, and rotating part of
connecting rod, J.sub.sq, may also be determined experimentally for
each gear. The load torque T.sub.L(.theta.) 476 may be estimated
from the difference between the engine speed and turbine shaft
speed through equation (18) for the torque converter and torque
converter clutch. T.sub.p is the torque converter torque and
T.sub.tCC is the torque converter clutch torque. K.sub.i is
calculated by a lookup table obtained from experiments and torque
converter clutch gain K.sub.tCC and a constant .alpha. may also be
determined experimentally.
T L = T p + T tcc T p = .omega. e - .omega. t .omega. e - .omega. t
.omega. e 2 K i 2 T tcc = K tcc tanh ( .omega. e - .omega. t
.alpha. ) ( 18 ) ##EQU00009##
The variables .omega..sub.e and .omega..sub.t are the angular speed
of crankshaft and turbine shaft, respectively. A discrete-time
low-pass filters may be applied to T.sub.p and T.sub.tCC to remove
high frequency components. The low-pass filter may be given by the
following transfer function
F ( z ) = b z - a ( 19 ) ##EQU00010##
where a and b are filter constants.
[0061] Equation (15) may be solved for {umlaut over (.theta.)}
using the measured crank angular velocity {dot over (.theta.)}
via
.theta. = 1 J eq + M eq r 2 f 1 f 3 [ - M eq r 2 f 2 f 3 .theta. .
2 + T i ( .theta. ) - T fp ( .theta. ) - T L ( .theta. ) ] ( 20 )
##EQU00011##
[0062] The predicted crank acceleration 486 obtained by the
Predicted Crankshaft Acceleration Module 480 using the model
described above may be compared with the measured crank angular
acceleration 488 determined by the Engine Parameter Measurement
Module 206 (e.g., step 106 of FIG. 1). Measured crank acceleration
488 may be computed from the measured crank angular speed in the
6-degree angle domain, where the crank angular speed is sampled at
every 6 crank angle degrees, by the following formulae to obtain
the derivative and also reduce the effect of measurement noise.
A time ( n ) = 42 k = 1 7 T d ( n - k ) - 42 k = 8 14 T d ( n - k )
k = 4 10 T d ( n - k ) ( 21 ) T d ( n ) = 6 360 r ( n ) 6 = 1 10 1
r ( n ) ( 22 ) ##EQU00012##
r(n) is the crank angular speed at time step n in 6 degree angle
domain. The acceleration formulae (21) can also be approximated as
the double average of acceleration shown below.
A rpm ( n ) = 1 7 k = 1 7 r ( n - k ) - 1 7 k = 8 14 r ( n - k ) k
= 4 10 T d ( n - k ) = 1 7 k = 1 7 1 7 m = 0 6 a ( n - k - m ) ( 23
) ##EQU00013##
[0063] Here the term T.sub.d(n) is treated as a constant during the
time steps considered and Euler's rule is used to derive the
relationship between r(n) and the acceleration a(n). FIG. 8 plots
the crank shaft acceleration versus time for an engine running
under substantially steady-state conditions. FIG. 8 compares the
two averaging methods, that based on Eq. (21), curve 810, and that
based on Eq. (23), curve 812, applied to the same angular speed
signal generated for validation purposes. The peaks in the curves
810 and 812 correspond to cylinder firings and the dips correspond
to skipped firing opportunities. For clarity the initial section of
curve 812 (dashed line) is omitted and the final section of curve
810 (solid line) is omitted. Inspection of FIG. 8 illustrates that
the difference between the two methods is negligible. This
comparison demonstrates that the acceleration obtained from the
engine dynamics model can be filtered in 6-degree domain and can be
compared with the measured acceleration obtained from Eq. (21).
[0064] A high-pass filter may then be applied to both measured and
modeled accelerations. The high-pass filter removes any mean value
offset errors that may be present in the acceleration estimate,
making it easier to compare the characteristics of the measured and
simulated accelerations relevant for high pressure exhaust spring
detection. The high-pass filter may be given by
y(z)=-a.sub.1y(n-1)-a.sub.0y(n-2)+b.sub.2x(n)+b.sub.1x(n-1)+b.sub.0x(n-2-
). (24)
where a.sub.0, a.sub.1, b.sub.0, b.sub.1, and b.sub.2 are the
appropriate filter coefficients determined by experimental data.
Based on the comparison of the measured and modeled accelerations,
the misfire detection module determines whether a misfire took
place (e.g., step 112 of FIG. 1.)
[0065] The misfire detection module may use a wide variety of
techniques to determine whether a misfire took place (step 112. In
some embodiments, for example, the misfire determination is based
at least in part on the following formula:
X = A - B A ##EQU00014##
where A is the expected change in the engine parameter (e.g., as
determined in step 110) and B is the measured change in the engine
parameter (e.g., as determined in step 106). If the value X exceeds
a particular predefined threshold, then the misfire determination
module determines that a misfire has (possibly) occurred. If the
value X does not exceed the predefined threshold, then the misfire
determination module determines that a misfire has not
occurred.
[0066] In some applications, the accuracy of the misfire
determination process may be improved by adjusting the above
formula as follows:
X = ( A - B A ' + k ) Z ##EQU00015##
where A' is a low-pass filtered mean of A. A' can also be an
expected change in the engine parameter and may be directly
proportional to mass air charge per working chamber. Z is any
suitable exponent e.g., in some applications, Z=3 works well. k is
a predefined threshold such that the value of X of 1 or greater
indicates a possible misfire, and the value of X of less than 1
indicates that a misfire has not occurred. In some implementations,
it has been determined that above adjustments can help reduce the
amount of error caused by the complexity of the pressure model
and/or improve the accuracy of the misfire determination
process.
[0067] Generally, when an instance of misfire is detected for a
particular working chamber in which the aforementioned misfire
threshold is exceeded, the information is stored in an additional
module not shown in FIG. 4 in which a misfire counter for that
working chamber is incremented. Typically, multiple firing events
are monitored in order to confirm that a working chamber has
misfired. In some embodiments, for example, the above misfire
determination techniques are executed for many, almost all, or all
firing events. Generally, a firing event involves an attempt to
actually fire a working chamber, as opposed to the skipping of the
working chamber. Each firing event is associated with the identity
of a particular working chamber and data indicating whether the
misfire threshold had been exceeded. This information is used to
build a database of firing events. Thus, the misfire detection
module 208 stores a history for each working chamber that indicates
the number of firing events in which the misfire threshold was
exceeded. In some embodiments, if a particular working chamber is
associated with multiple firing events of which at least a
predetermined percentage or number involves the exceeding of a
misfire threshold, a determination is made that the working chamber
is misfiring and the appropriate error signal is communicated to
the vehicle driver via the OBD system, typically a malfunction
indicator lamp on the vehicle dashboard. An appropriate error code
may also be sent to the OBD interface for subsequent diagnostic
evaluation.
[0068] It should be appreciated that the misfire determination
process is not limited to the aforementioned formulas, and that any
suitable technique for determining misfire may be used. In various
embodiments, for example, an adjusted version of the above formulas
is used e.g., the misfire determination involves exponentiation of
a value based on A, B and A', but the value and the aforementioned
variables or formulas may be further adjusted in various ways not
explicitly described above.
[0069] After a particular working chamber is determined to be
misfiring as indicated above, additional steps may be taken. Such
steps include but are not limited to the skipping of the misfiring
working chamber, the displaying of an alert and the use of a fixed
firing sequence. These and other steps are described in co-assigned
U.S. patent application Ser. No. 14/207,109 (hereinafter referred
to as the '109 application), which is incorporated herein in its
entirety for all purposes. Any of the above techniques described in
the '109 application may be performed after the steps of method 100
of FIG. 1 are performed.
[0070] The arrangements and techniques described in FIGS. 1-4 can
be used for a variety of applications. In various embodiments, the
illustrated misfire detection system 200 (FIG. 2) is stored in an
engine control unit of a vehicle and/or is part of an onboard
diagnostics system. In other embodiments, it may be stored in an
external diagnostic device that is used to examine the performance
of an engine. Any of the aforementioned modules, systems and
operations may be stored in the form of hardware, software or
both.
[0071] Referring next to FIG. 9, an example method 900 for using an
adaptive model will be described. As discussed above in connection
with method 100 of FIG. 1, for various applications, it is useful
to use a model (e.g., a pressure or torque model) to estimate a
change in an engine parameter (e.g., crankshaft acceleration)
during a particular window. This estimate may be used to help
determine whether any engine errors have taken place. However, in
some cases, possibly due to unforeseen conditions and the various
assumptions that the model is based on, the estimate provided by
the model may be inaccurate. For example, as an engine ages leakage
past the piston rings and valve seats may impact the pressures and
associated torque generated by a cylinder. To improve the accuracy
of the model, the engine parameter is measured during the same
window and the model is adjusted based on the measurement. Method
900 describes an example of this approach. The techniques described
in method 900 may be applied to any of the aforementioned methods
(e.g., method 100 of FIG. 1) and may be performed in skip fire or
conventional engine control systems.
[0072] Initially, at step 402, firing information is obtained. At
step 404, a window is assigned to a target firing opportunity. At
step 406, a change in an engine parameter (e.g., crankshaft
acceleration) is measured. At step 408, a model is used to estimate
an expected change in the engine parameter. The model may be any
suitable model used to estimate a change in the engine parameter
(e.g., a model that estimates pressure within and/or torque
generated by each working chamber as described in method 100 of
FIG. 1, FIG. 4, etc.) Steps 402, 404, 406 and 408 may be performed
in the same manner as steps 102, 104, 106 and 108 of FIG. 1,
respectively.
[0073] At step 410, the model is adjusted based on a comparison
between the expected change in the engine parameter (step 408) and
the measured change in the engine parameter (step 406). In various
embodiments, this adjustment is only performed when the difference
between the expected change and the measured change exceeds a
predefined threshold. The adjustment may be performed in a variety
of ways. In some embodiments, for example, when steps 406 and 408
are repeated at a later time, a multiplier is applied to the
expected change determined using the model. The multiplier reduces
the offset between the measured and expected values. Put another
way, when step 408 is repeated and the model generates another
estimate of an expected change in the engine parameter, the
estimate is adjusted to bring it more in line with a corresponding
measurement of the engine parameter.
[0074] An example of this approach is illustrated in FIGS. 10 and
11. FIG. 10 is a graph illustrating crankshaft acceleration as a
function of time in an example implementation of the aforementioned
model. In the illustrated embodiment of FIG. 10, the model has not
been adjusted based on the measurements performed in step 406. The
solid line curve indicates the crankshaft acceleration over time as
estimated using the model. The dotted line curve indicates
measurements of the crankshaft acceleration over time. The graphs
indicate a mismatch between the dotted line and solid line curves.
That is, the crankshaft acceleration estimated by the model tends
to significantly overshoot the measured crankshaft
acceleration.
[0075] In FIG. 11, the model is adjusted as described in step 410
based on a comparison of the results illustrated in FIG. 10. In
FIG. 11, the difference between the expected and measured changes
in the crankshaft acceleration are thus significantly reduced. That
is, the solid line curve (which represents the crankshaft
acceleration estimated by the model) more closely approximates the
dotted line curve (which represents the measured crankshaft
acceleration.) Put another way, the offset between the expected
engine parameter change (e.g., from step 408) generated by the
model and the measured engine parameter change (e.g., from step
406) has been reduced. It should be appreciated that this approach
does not cause a problem in detecting an engine error, such as a
misfire event, which is marked in the graph. At that point in time,
the measured crankshaft acceleration is much lower than what was
predicted by the model. This difference may be used to identify a
possible misfire (e.g., as previously discussed in connection with
steps 108 and 110 of FIG. 1.)
[0076] The adjustment of the model may be performed in any suitable
manner A particular embodiment is illustrated in FIG. 12. FIG. 12
is a flow diagram illustrating how an adaptive model may be used to
estimate a change in crankshaft acceleration during a particular
window. The diagram indicates various calculations that can be
performed to generate the estimate (e.g., step 408.) Section 1204
of the flow diagram compares one or more past measurements of
changes in crankshaft acceleration (e.g., step 406) and one or more
past estimates of the changes in crank acceleration based on the
model (e.g., step 408). At multiplier block 1206, a suitable
multiplier is applied to one or more Crank Accel model input
parameters 1208 based on the comparison. The adjusted modeled
inputs 1202 may be used in the model 1210 to yield an adjusted
modeled crank acceleration 1212. Filtered adjusted modeled crank
acceleration 1212 may be used as a feedback signal to section 1204
and used in a misfire detection algorithm, for example the
algorithm depicted in FIG. 9.
[0077] In addition to a skip fire controlled engine, the methods
and arrangements described here are applicable to other engine
control methods that may have significantly different torque
signatures associated with sequential firing opportunities. The
individual cylinder control concepts used in dynamic skip fire can
also be applied to dynamic multi-charge level engine operation in
which all cylinders are fired, but individual working cycles are
purposely operated at different cylinder output levels. Dynamic
skip fire and dynamic multi-charge level engine operation may
collectively be considered different types of dynamic firing level
modulation engine operation in which the output of each working
cycle (e.g., skip/fire, high/low, skip/high/low, etc.) is
dynamically determined during operation of the engine, typically on
an individual cylinder working cycle by working cycle (firing
opportunity by firing opportunity) basis. These control methods and
arrangements are described in more detail in U.S. Pat. No.
9,689,327, which is incorporated herein by reference in its
entirety for all purposes.
[0078] As noted earlier, the pressure model described herein is
applicable to many types of engine cycles, including, for example,
a Miller or Atkinson cycle where cylinder air charge is reduced by
either an early intake valve closing (EIVC) or late intake valve
closing (LIVC). The model is thus applicable to dynamic firing
level modulation controlled engines, where either multi-stage cam
lift profiles or variable cam timing are used on different firing
opportunities to induct differing amount of mass air charge into
the cylinders. Relevant parameters for each cam profile can be
incorporated in the pressure model. Additionally, variations in
combustion stoichiometery, such as some firing opportunities using
a lean burn air-fuel ratio may be included in the pressure model.
Depending on the thermodynamic cycle, the thermodynamic state at
IVC, such as P.sub.IVC (pressure at IVC) and T.sub.IVC (temperature
at IVC) will be different modifying the shape of the P-V diagram
shown in FIG. 6. The reference state at WC may be determined from
experimental data by, for example, using a neural network or other
machine learning approach that may include regression analysis to
help determine the statistical relationship between the various
model parameters. It should be appreciated that many of the
variables used in Equations (1-9) such as, but not limited to, fuel
mass, total fuel and air mass, combustion parameter alpha, start of
combustion, combustion duration, and/or conversion efficiency may
be different depending on the type of combustion cycle.
[0079] The described methods and arrangements may also be
integrated into a hybrid powertrain where the crankshaft may be
driven by a combination of an internal combustion engine and some
auxiliary power source, such as an electric motor. In general, the
auxiliary power source may at various times add or subtract torque
from the powertrain crankshaft depending on the control settings.
For example, an electric motor/generator may at times be used as an
electric generator to store energy drawn from the powertrain in an
energy storage device such as a capacitor or a battery, and may at
times be used as an electric motor drawing energy from the energy
storage device and adding torque to the powertrain.
[0080] To include an auxiliary power source in a misfire detection
system FIG. 4, can be modified to include such an additional torque
source/sink. The resultant misfire detection system is shown in
FIG. 13. A signal 472 from an auxiliary power source control module
470 is directed into the predicted crankshaft acceleration module
480. The signal 472 is a time or crank angle based estimate of the
torque added or subtracted from the crankshaft by the auxiliary
power source.
[0081] To model the impact of the auxiliary power source on
crankshaft rotation, some of the preceding equations used to
predict a misfire may be modified to include the impact of an
auxiliary power source on the crankshaft rotation. For example, a
term representing the auxiliary power source torque, such as an
electric motor/generator torque (L.sub.mt(.theta.)), may be added
to Equation (15) yielding Equation (25).
j.sub.eq{umlaut over
(.theta.)}+M.sub.eqr.sup.2[f.sub.1(.theta.){umlaut over
(.theta.)}+f.sub.2(.theta.){dot over
(.theta.)}.sup.2]f.sub.3(.theta.)=T.sub.i(.theta.)-T.sub.fp(.theta.)-T.su-
b.L(.theta.)+T.sub.mt(.theta.) (25)
[0082] Equation (25) for the predicted crankshaft angular
acceleration may be solved in an analogous manner to that
previously described for Equation (15) to yield Equation (26),
which is analogous to Equation (20) with the addition of the
auxiliary power source torque.
.theta. = 1 J eq + M eq r 2 f 1 f 3 [ - M eq r 2 f 2 f 3 .theta. .
2 + T i ( .theta. ) - T fp ( .theta. ) - T L ( .theta. ) + T mt (
.theta. ) ] ( 26 ) ##EQU00016##
[0083] As described earlier, the predicted crank acceleration 486
obtained by the Predicted Crankshaft Acceleration Module 480 using
the model described above may be compared with the measured crank
angular acceleration 488 determined by the Engine Parameter
Measurement Module 206 (e.g., step 106 of FIG. 1). In this case the
impact of the auxiliary power source on an engine parameter in the
target window must be included in step 106 of FIG. 1 in addition to
the impact of internal combustion engine. The engine parameter may
be crankshaft acceleration. If the predicted crankshaft angular
acceleration 486 and the measured crankshaft angular acceleration,
or some factor based on the two quantities, differ by more than a
predefined threshold, the misfire detection system may determine
that a misfire has occurred. Similarly, if the two quantities, or
some factor based on the two quantities, are within a predefined
threshold, the misfire detection may determine that no misfire has
occurred.
[0084] The described methods and arrangements may be integrated
into any suitable skip fire engine control system. It should be
appreciated that the described misfire detection system 200 may
include additional components, features or modules that are not
show in FIG. 2. For example, the firing sequences generated by the
firing timing determination module 202 may be based on a firing
fraction. In some embodiments, the misfire detection system 200
includes a firing fraction calculator that determines this firing
fraction based on a desired torque. A wide variety of firing
fraction calculators, firing timing determination modules,
powertrain parameter adjusting modules, ECUs, engine controller and
other modules are described in co-assigned U.S. Pat. Nos.
7,954,474; 7,886,715; 7,849,835; 7,577,511; 8,099,224; 8,131,445;
and 8,131,447; U.S. patent application Ser. Nos. 13/774,134;
13/963,686; 13/953,615; 13/953,615; 13/886,107; 13/963,759;
13/963,819; 13/961,701; 13/963,744; 13/843,567; 13/794,157;
13/842,234; 13/004,839, 13/654,244 and 13/004,844; and U.S.
Provisional Patent Application Nos. 61/080,192; 61/104,222; and
61/640,646, each of which is incorporated herein by reference in
its entirety for all purposes. Various engine diagnostic and
misfire detection techniques are described in U.S. Provisional
Patent Application Nos. 61/799,180 and 61/002,762 and U.S. patent
application Ser. No. 14/207,109, which are also incorporated herein
by reference in their entirety for all purposes. Any of the
features, modules and operations described in the above patent
documents may be added to the illustrated misfire detection system
200. In various alternative implementations, these functional
blocks may be accomplished algorithmically using a microprocessor,
ECU or other computation device, using analog or digital
components, using programmable logic, using combinations of the
foregoing and/or in any other suitable manner
[0085] Any and all of the described components may be arranged to
refresh their determinations/calculations very rapidly. In some
preferred embodiments, these determinations/calculations are
refreshed on a firing opportunity by firing opportunity basis
although that is not a requirement. In some embodiments, for
example, the described engine parameter change measurements, the
adaptive adjustment of a model (e.g., step 410 of FIG. 4) and the
misfire/engine error determinations are performed on a firing
opportunity by firing opportunity basis. An advantage of firing
opportunity by firing opportunity operation of the various
components is that it makes the controller very responsive to
changed inputs and/or conditions. Although firing opportunity by
firing opportunity operation is very effective, it should be
appreciated that the various components can be refreshed more
slowly while still providing good control (e.g., the
determinations/calculations may be performed every revolution of
the crankshaft, every one or more working cycles, etc.).
[0086] The invention has been described primarily in the context of
detecting misfire in the skip fire operation of 4-stroke piston
engines suitable for use in motor vehicles. However, it should be
appreciated that the described misfire detection approaches are
very well suited for use in a wide variety of internal combustion
engines. These include engines for virtually any type of
vehicle--including cars, trucks, boats, aircraft, motorcycles,
scooters, etc.; and virtually any other application that involves
the firing of working chambers and utilizes an internal combustion
engine. The various described approaches work with engines that
operate under a wide variety of different thermodynamic
cycles--including virtually any type of two stroke piston engines,
diesel engines, Otto cycle engines, Dual cycle engines, Miller
cycle engines, Atkinson cycle engines, Wankel engines and other
types of rotary engines, mixed cycle engines (such as dual Otto and
diesel engines), hybrid engines, radial engines, etc. It is also
believed that the described approaches will work well with newly
developed internal combustion engines regardless of whether they
operate utilizing currently known, or later developed thermodynamic
cycles.
[0087] In some embodiments, the firing timing determination module
utilizes sigma delta conversion to generate a skip fire firing
sequence. Although it is believed that sigma delta converters are
very well suited for use in this application, it should be
appreciated that the modules may employ a wide variety of
modulation schemes. For example, pulse width modulation, pulse
height modulation, code division multiple access (CDMA) oriented
modulation or other modulation schemes may be used to deliver the
drive pulse signal. Some of the described embodiments utilize first
order converters. However, in other embodiments higher order
converters may be used. In still other embodiments, as described in
some of the aforementioned patent documents, a firing sequence is
selected from a library of predefined firing sequences.
[0088] It should be also appreciated that any of the operations
described herein may be stored in a suitable computer readable
medium in the form of executable computer code. The operations are
carried out when a processor executes the computer code. Such
operations include but are not limited to any and all operations
performed by the firing timing determination module 202, the firing
control unit 204, the engine parameter measurement module 206, the
misfire detection module 208, the misfire detection system 200, or
any other module, component or controller described in this
application.
[0089] The described embodiments work well with skip fire engine
operation. In some implementations, working chambers are fired
under close to optimal conditions. That is, the throttle may be
kept substantially open and/or held at a substantially fixed
positioned and the desired torque output is met by varying the
firing frequency. In some embodiments, during the firing of working
chambers the throttle is positioned to maintain a manifold absolute
pressure greater than 70, 80, 90 or 95 kPa.
[0090] In some embodiments, the above techniques make use of the
actual firing history of the cylinders so that only fired cylinders
are actually considered by the misfire detection system. That is,
when a cylinder is skipped, no effort is made to detect a misfire
event with respect to that specific cylinder (e.g., the method of
FIG. 1 is applied such that the target firing opportunity always
involves a target working chamber that was arranged to be fired
during the assigned window and not skipped.) In this way, the lack
of the acceleration peaks during the timeslots associated with the
missed firing opportunities will not be interpreted as misfires of
the associated cylinders.
[0091] Various embodiments of the invention have been primarily
described in the context of a skip fire control arrangement in
which cylinders are deactivated during skipped working cycles by
deactivating both the intake and exhaust valves in order to prevent
air from being pumped through the cylinders during skipped working
cycles. However, it should be appreciated that some skip fire valve
actuation schemes contemplate deactivating only exhaust valves, or
only the intake valves to effectively deactivate the cylinders and
prevent the pumping of air through the cylinders. Several of the
described approaches work equally well in such applications.
Further, although it is generally preferable to deactivate
cylinders, and thereby prevent the passing of air through the
deactivated cylinders during skipped working cycles, there are some
specific times when it may be desirable to pass air through a
cylinder during a selected skipped working cycle. By way of
example, this may be desirable when engine braking is desired
and/or for specific emissions equipment related diagnostic or
operational requirements. The described valve control approaches
work equally well in such applications.
[0092] Various implementations of the invention are very well
suited for use in conjunction with dynamic skip fire operation in
which an accumulator or other mechanism tracks the portion of a
firing that has been requested, but not delivered, or that has been
delivered, but not requested such that firing decisions may be made
on a firing opportunity by firing opportunity basis. However the
described techniques are equally well suited for use in virtually
any skip fire application (operational modes in which individual
cylinders are sometimes fired and sometime skipped during operation
in a particular operational mode) including skip fire operation
using fixed firing patterns or firing sequences as may occur when
using rolling cylinder deactivation and/or various other skip fire
techniques. Similar techniques may also be used in variable stroke
engine control in which the number of strokes in each working cycle
are altered to effectively vary the displacement of an engine.
[0093] Although only a few embodiments of the invention have been
described in detail, it should be appreciated that the invention
may be implemented in many other forms without departing from the
spirit or scope of the invention. FIGS. 1 and 4, for example,
illustrate a number of steps in a method for detecting misfire or
other engine errors. It should be appreciated that these operations
need not take place in the illustrated order, and one or more steps
may be modified, reordered, removed or replaced. There are also
several references to the term, "cylinder." It should be understood
that the term cylinder should be understood as broadly encompassing
any suitable type of working chamber. Therefore, the present
embodiments should be considered illustrative and not restrictive
and the invention is not to be limited to the details given
herein.
* * * * *